Currently, R-T-B based (where R is at least one of the rare-earth elements including Y, T is a transition metal including iron as its main ingredient, and B is boron) rare-earth magnets are extensively used as high-performance magnets in a broad variety of applications. In order to not just save, or at least use more efficiently, valuable natural resources but also cut down the manufacturing cost of the R-T-B based rare-earth magnets, it is important to make those R-T-B based rare-earth magnets recyclable.
The grinding sludge and fine powder, which are produced during the manufacturing process of R-T-B based sintered magnets, are oxidizable so easily as to possibly ignite spontaneously within the air atmosphere. Accordingly, the sludge and fine powder are normally oxidized intentionally by incineration or any other suitable process so as to turn into chemically stabilized oxides. If those oxides are subjected to a chemical process such as acid dissolution, the rare-earth components thereof can be separated and extracted.
Meanwhile, techniques of recycling final R-T-B based magnet products into the R-T-B based material alloy by re-melting or any other process are also under research and development.
However, if the R-T-B based rare-earth magnets are re-melted, then oxygen can be sufficiently removed from the rare-earth magnets but the carbon content thereof rather increases. Other problems may also be caused by the re-melting technique.
It has been generally believed that to improve the magnet performance and anticorrosiveness of R-T-B based rare-earth magnets, impurities such as oxygen and carbon should be eliminated from the magnets as much as possible. According to this point of view, the technique of removing those impurities is a key to making the R-T-B based rare-earth magnets recyclable more easily and more effectively.
However, if a special process is required to remove oxygen and carbon, then the manufacturing cost will rise significantly and cannot be reduced effectively. This constitutes a serious obstacle to recycling the rare-earth magnets successfully.
In attempting to recycle a rare-earth bonded magnet on the other hand, the bonded magnet may be separated into a magnetic powder and a binder resin, and then only the magnetic powder may be subjected to a recycling process. According to this technique, however, such a resin includes too much carbon component to prevent the carbon in the resin from depositing or sticking onto the magnetic powder. Thus, the magnetic powder collected from the bonded magnet should include a lot of carbon and other impurities. For that reason, the bonded magnets, as well as the rare-earth sintered magnets, also require a special carbon removal process, thus making the rare-earth bonded magnets non-recyclable.
In order to overcome the problems described above, a primary object of the present invention is to provide an R-T-B-C based rare-earth alloy magnetic material, which includes carbon (C) as an indispensable element but can still exhibit excellent magnetic properties, while making rare-earth magnets recyclable.